1. Field of the Invention
This invention relates to an improved differential pressure transmitter that comprises a linear air velocity transmitter and to a pneumatically operated square root extractor device for such a transmitter or the like. This invention also relates to methods of making such a transmitter and/or such a square root extractor device.
2. Prior Art Statement
It is known to provide a differential pressure transmitter having means for producing an output pneumatic signal from a pneumatic source in relation to the air velocity pressure of air flowing in a passage defining means as defined by means of the transmitter that senses the difference between the total pressure and the static pressure of the air flowing in the passage defining means.
However, such output signal is non-linear with respect to the air velocity and in order to provide a linear signal, it is necessary to linearize the output pressure signal of the differential pressure transmitter by directing the output pneumatic signal of the transmitter to the input port of a separate square root extractor device which extracts the square root from the input pneumatic signal thereto to provide a linear output pneumatic signal.
For example, two such known separate pneumatically operated square root extractors are described in the following two publications:
(1) Page 7 of the operating manual entitled Operating Manual "Force Bridge", of Sorteberg Controls Company, South Norwalk, Conn.
(2) Pages 1 and 2 of the Technical Information Bulletin TI 37-55B, dated August, 1969, and entitled "557 Series Pneumatic Square Root Extractor" of The Foxboro Company, Foxboro, Mass.
It appears that the pneumatically operated square root extractor of Item (1) above moves a pair of rollers between a pair of flapper levers disposed in parallel relation and respectively controlling a pair of bleed nozzles, the pair of rollers being driven in unison by a pneumatically operated movable wall means to change the fulcrum points of the flapper levers and thereby extracting the square root from the input pneumatic signal.
It appears that the pneumatic square root extractor of Item (2) above has a flapper lever controlling a bleed nozzle and being interconnected to a flexure point which has the flexure angle thereof changed by a movable wall so as to extract the square root from the input pneumatic signal.